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Motorola MaxTrac VHF RX problem - Please Help!

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Motorola MaxTrac VHF RX problem - Please Help!

Postby sarcomguy » Wed May 06, 2009 6:51 pm

Hi, I am having a problem with a Motorola MaxTrac VHF 32Ch Mobile, that I use for Search & Rescue. Any help would be greatly appreciated. The problem is, it will not receive, but it transmits perfectly. The sound works fine, it has the jumpers, the antenna and coax work fine; I double checked them on another MaxTrac and that works fine, it’s not near the power supply, and I can hear the tones from changing channels etc. But it will not receive on the channels. Does anyone have any advice?

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What radios do you own?: Motorola, Icom, Sunair (HF).

Re: Motorola MaxTrac VHF RX problem - Please Help!

Postby kc7gr » Wed May 06, 2009 7:41 pm

Could be any number of factors. Some of the more common problems include severe reduction in receiver sensitivity due to blown PIN diodes in the antenna switch section; failure of the first local oscillator crystal; and failure of the audio stage due to one or the other speaker lead getting shorted to ground.

No matter what, the symptom you describe is going to need test gear, tools, and a service manual to troubleshoot. If you lack any or all the above, I can work on the unit for you at my normal rate (see for details).

If you do have access to a service monitor and test bench, the first thing I would try is generate a signal on the thing's normal receive frequency, and keep upping the level into the antenna jack until about 0dBm. If it starts hearing the signal at high levels, I would suspect the PIN diodes.

Next, try generating a signal on the first IF frequency, inject it at the right point, and see if the receiver will pick it up. You can also try generating and injecting a signal at the second IF frequency and see if the receiver will hear it.

Happy tweaking.
Bruce Lane, KC7GR
"Raf tras spintern. Raf tras spoit."

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Re: Motorola MaxTrac VHF RX problem - Please Help!

Postby jackhackett » Thu May 07, 2009 5:22 am

usually the 44.645MHz 2nd oscillator crystal.

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